In recent years, accompanying the digitalization of electronic equipment, there has been a growing demand for reductions in the high-frequency region impedance (the equivalent series resistance (hereafter also abbreviated as ESR)) of the condensers used in the electronic equipment. Conventionally, in order to satisfy these demands, so-called functional condensers (hereafter abbreviated to simply “condensers”) that use an oxide film of a valve metal such as aluminum, tantalum or niobium as a dielectric body have been used.
As disclosed in Patent Document 1, the structures of these condensers typically include an anode composed of a porous body of a valve metal, a dielectric layer formed by oxidizing the surface of the anode, a conductive solid electrolyte layer, and a cathode on which is laminated a carbon layer or a silver layer or the like. A conductive film containing a π-conjugated conductive polymer may be used as the solid electrolyte layer.
Widely known processes for forming a conductive film containing a π-conjugated conductive polymer include electrolytic polymerization processes in which a conductive layer composed of a manganese oxide is formed in advance on the surface of a valve metal porous body, and this conductive layer is then used as an electrode for performing the electrolytic polymerization (see Patent Document 2), and chemical oxidative polymerization processes in which a precursor monomer that generates the π-conjugated conductive polymer is polymerized using an oxidant (see Patent Document 3).
As a process for forming a conductive film other than the electrolytic polymerization process and chemical oxidative polymerization process described above, a process has been proposed in which aniline is subjected to a chemical oxidative polymerization in the presence of a polyanion having, for example, a sulfo group and a carboxyl group, thereby forming a water-soluble polyaniline, and then applying and drying an aqueous solution of the polyaniline to form a coating (see Patent Document 4). With this process, a conductive film with a high degree of conductivity can be formed relatively simply.
Further, condensers require a high capacitance. In order to achieve a high capacitance, a process has been proposed in which, by finely controlling the temperature conditions of the chemical oxidative polymerization, the solid electrolyte layer can be formed satisfactorily within the interior of the dielectric layer (see Patent Document 5).
Moreover, in order to prevent shorting between the anode and the solid electrolyte layer, a solid electrolytic condenser has been proposed in which a polyimide silicone layer is first formed on the surface of the dielectric layer, and an oxidative polymerization process is then used to form a conductive polymer layer (see Patent Document 6).
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. 2003-37024
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. Sho 63-158829
[Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. Sho 63-173313
[Patent Document 4]
Japanese Unexamined Patent Application, First Publication No. Hei 7-105718
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. Hei 11-74157
[Patent Document 6]
Japanese Unexamined Patent Application, First Publication No. 2005-109079